High performance alloys with improved metal dusting corrosion resistance

ABSTRACT

Alloy compositions which are resistant to metal dusting corrosion are provided by the present invention. Also provided are methods for preventing metal dusting on metal surfaces exposed to carbon supersaturated environments. The alloy compositions include an alloy (PQR), and a multi-layer oxide film on the surface of the alloy (PQR). The alloy (PQR) includes a metal (P) selected from the group consisting of Fe, Ni, Co, and mixtures thereof, an alloying metal (Q) comprising Cr, Mn, and either Al, Si, or Al/Si, and an alloying element (R). When the alloying metal (Q) includes Al, the multi-layer oxide film on the surface of the alloy includes at least three oxide layers. When the alloying metal (Q) includes Si, the multi-layer oxide film on the surface of the alloy (PQR) includes at least four oxide layers. When the alloying metal (Q) includes Al and Si, the multi-layer oxide film on the surface of the alloy (PQR) includes at least three oxide layers. The multi-layer oxide film is formed in situ during use of the alloy composition in a carbon supersaturated metal dusting environment. Advantages exhibited by the disclosed alloy compositions include improved metal dusting corrosion resistance at high temperatures in carbon-supersaturated environments having relatively low oxygen partial pressures. The disclosed alloy compositions are suitable for use as the inner surfaces in reactor systems and refinery apparatus.

FIELD OF THE INVENTION

The present invention relates to the field of materials used inhydrocarbon conversion processes. It more particularly relates tomaterials exposed to corrosive reactants and carbon supersaturatedenvironments. Still more particularly, the present invention relates toalloy compositions and methods for controlling metal dusting corrosionin reactor systems and refinery apparatus exposed to high carbonactivities and relatively low oxygen activities.

BACKGROUND OF THE INVENTION

In many hydrocarbon conversion processes, for example the conversion ofmethane to syngas, environments are encountered that have high carbonactivities and relatively low oxygen activities. High temperaturereactor materials and heat exchanger materials used in such processescan deteriorate in service by a very aggressive form of corrosion knownas metal dusting. Metal Dusting is a deleterious form of hightemperature corrosion experienced by Fe, Ni and Co-based alloys attemperatures in the range, 350-1050° C. in carbon-supersaturated (carbonactivity>1) environments having relatively low (about 10⁻¹⁰ to about10⁻²⁰ atmospheres) oxygen partial pressures. This form of corrosion ischaracterized by the disintegration of bulk metal into powder or dust.

Although many high temperature alloys are designed to form an in-situsurface film of chromium oxide (Cr₂O₃) in low oxygen partial pressureenvironments, the nucleation and growth kinetics of this oxide are oftennot fast enough to prevent carbon intrusion in highly reducingcarbon-rich environments with carbon activities in excess of unity.Furthermore, the formation of a Cr₂O₃ film provides initial protectionagainst carbon ingress. The alloy is protected from carbon ingress in asmuch as the carbon does not migrate through the oxide film. However, thepresence of deflects and differential thermal contraction between thealloy and an oxide during oxide film growth could induce stresses thatmay result in rupture of the oxide film. Such local rupture of the oxidefilm would lead to carbon migration into the steel.

Methodologies disclosed in the literature for controlling metal dustingcorrosion involve the use of surface coatings and gaseous inhibitors,for example H₂S. Coatings can degrade by inter diffusion of the coatingconstituents into the alloy substrate. Thus, while coatings are a viableapproach for short-term protection, they are generally not advisable fora long term service life of twenty years or more. Inhibition by H₂S alsohas two disadvantages. One is that H₂S tends to poison most catalystsused in hydrocarbon conversion processes. Secondly, H₂S has to beremoved from the exit stream which can substantially add to processcosts.

U.S. Pat. No. 6,692,838 to Ramanarayanan et al. discloses compositionsresistant to metal dusting and a method for preventing metal dusting onmetal surfaces exposed to carbon supersaturated environments. Thecompositions comprise (a) an alloy, and (b) a protective oxide coatingon the alloy. The alloy comprises alloying metals and base metals,wherein the alloying metals comprise a mixture of chromium andmanganese, and the base metal comprises iron, nickel, and cobalt. U.S.Pat. No. 6,692,838 is incorporated herein by reference in its entirety.

A need exists for an advanced alloy composition that is resistant tometal dusting corrosion in low (about 10⁻¹⁰ to about 10⁻²⁰ atmospheres)oxygen partial pressure and carbon-supersaturated (carbon activity>1)environments. Ideally, such an advanced alloy composition would becapable of rapidly forming an outer protective oxide film to blockcarbon transfer while growing an adherent inert oxide film slowly to actas a diffusion harrier to carbon ingress.

SUMMARY OF THE INVENTION

According to the present disclosure, an advantageous alloy compositionresistant to metal dusting corrosion comprises: a) an alloy (PQR) havinga surface, wherein P is a metal selected from the group consisting ofFe, Ni, Co, and mixtures thereof, Q is an alloying metal comprising Cr,Mn, and Al, and R is an alloying element, and b) a multi-layer oxidefilm on said surface of said alloy (PQR), wherein said multi-layer oxidefilm comprises at least three oxide layers, wherein a first oxide layercomprises an oxide selected from the group consisting of a manganeseoxide, a manganese chromate, a chromium oxide, and mixtures thereof, andis located adjacent to a third oxide layer, a second oxide layercomprises aluminum oxide, and is located between the surface of saidalloy (PQR) and said third oxide layer, and said third oxide layercomprises manganese aluminum oxide, and is located between said firstoxide layer and said second oxide layer.

A further aspect of the present disclosure relates to an advantageousalloy composition resistant to metal dusting corrosion comprising: a) analloy (PQR) having a surface, wherein P is a metal selected from thegroup consisting of Fe, Ni, Co, and mixtures thereof, Q is an alloyingmetal comprising Cr, Mn, and Si, and R is an alloying element, and b) amulti-layer oxide film on said surface of said alloy (PQR), wherein saidmulti-layer oxide film comprises at least four oxide layers, wherein afirst oxide layer comprises manganese oxide, and is located adjacent toa second oxide layer, said second oxide layer comprises an oxideselected from the group consisting of a manganese chromate, a chromiumoxide and mixtures thereof, and is located between said first oxidelayer and a fourth oxide layer, a third oxide layer comprises siliconoxide, and is located between said fourth oxide layer and said alloy(PQR), and said fourth oxide layer comprises manganese silicon oxide,and is located between said second oxide layer and said third oxidelayer.

A further aspect of the present disclosure relates to an advantageousalloy composition resistant to metal dusting corrosion comprising: a) analloy (PQR) having a surface, wherein P is a metal selected from thegroup consisting of Fe, Ni, Co, and mixtures thereof, Q is an alloyingmetal comprising Cr, Mn, Al, and Si, and R is an alloying element, andb) a multi-layer oxide film on said surface of said alloy (PQR), whereinsaid multi-layer oxide film comprises at least three oxide layers,wherein a first oxide layer comprises an oxide selected from the groupconsisting of a manganese oxide, a manganese chromate, a chromium oxide,and mixtures thereof, and is an outer layer located adjacent to a thirdoxide layer, a second oxide layer comprises aluminum oxide, siliconoxide, a solid solution of aluminum oxide and silicon oxide, andmixtures thereof, and is located between the surface of said alloy (PQR)and said third oxide layer, and said third oxide layer comprisesmanganese aluminum oxide, manganese silicon oxide, and mixtures thereof,and is located between said first oxide layer and said second oxidelayer.

A further aspect of the present disclosure relates to an advantageousmethod of preventing metal dusting of metal surfaces exposed to carbonsupersaturated environments comprising the step of providing a metalsurface with an alloy composition resistant to metal dusting corrosion,wherein said alloy composition comprises: a) an alloy (PQR) having asurface, wherein P is a metal selected from the group consisting of Fe,Ni, Co, and mixtures thereof, Q is an alloying metal comprising Cr, Mn,and Al, and R is an alloying element, and b) a multi-layer oxide film onsaid surface of said alloy (PQR), wherein said multi-layer oxide filmcomprises at least three oxide layers, wherein a first oxide layercomprises an oxide selected from the group consisting of a manganeseoxide, a manganese chromate, a chromium oxide, and mixtures thereof, andis located adjacent to a third oxide layer, a second oxide layercomprises aluminum oxide, and is located between the surface of saidalloy (PQR) and said third oxide layer, and said third oxide layercomprises manganese aluminum oxide, and is located between said firstoxide layer and said second oxide layer.

Another aspect of the present disclosure relates to an advantageousmethod of preventing metal dusting of metal surfaces exposed to carbonsupersaturated environments comprising the step of providing a metalsurface with an alloy composition resistant to metal dusting corrosion,wherein said composition comprises: a) an alloy (PQR) having a surface,wherein P is a metal selected from the group consisting of Fe, Ni, Co,and mixtures thereof, Q is an alloying metal comprising Cr, Mn, and Si,and R is an alloying element, and b) a multi-layer oxide film on saidsurface of said alloy (PQR), wherein said multi-layer oxide filmcomprises at least four oxide layers, wherein a first oxide layercomprises manganese oxide, and is located adjacent to a second oxidelayer, said second oxide layer comprises an oxide selected from thegroup consisting of a manganese chromate, a chromium oxide and mixturesthereof, and is located between said first oxide layer and a fourthoxide layer, a third oxide layer comprises silicon oxide, and is locatedbetween said fourth oxide layer and said alloy (PQR), and said fourthoxide layer comprises manganese silicon oxide, and is located betweensaid second oxide layer and said third oxide layer.

Another aspect of the present disclosure relates to an advantageousmethod of preventing metal dusting of metal surfaces exposed to carbonsupersaturated environments comprising the step of providing a metalsurface with an alloy composition resistant to metal dusting corrosion,wherein said composition comprises: a) an alloy (PQR) having a surface,wherein P is a metal selected from the group consisting of Fe, Ni, Co,and mixtures thereof. Q is an alloying metal comprising Cr, Mn, Al, andSi, and R is an alloying element, and b) a multi-layer oxide film onsaid surface of said alloy (PQR), wherein said multi-layer oxide filmcomprises at least three oxide layers, wherein a first oxide layercomprises an oxide selected from the group consisting of a manganeseoxide, a manganese chromate, a chromium oxide, and mixtures thereof, andis an outer layer located adjacent to a third oxide layer, a secondoxide layer comprises aluminum oxide, silicon oxide, and solid solutionof aluminum oxide and silicon oxide, and mixtures thereof, and islocated between the surface of said alloy (PQR) and said third oxidelayer, and said third oxide layer comprises manganese aluminum oxide,manganese silicon oxide, and mixtures thereof, and is located betweensaid first oxide layer and said second oxide layer.

Numerous advantages result from the advantageous alloy compositionresistant to metal dusting corrosion comprising a) an alloy (PQR), andb) a multi-layer oxide film on the surface of the alloy (PQR) disclosedherein and the uses/applications therefore.

For example, in exemplary embodiments of the present disclosure, thedisclosed alloy composition comprising an alloy (PQR), and a multi-layeroxide film on the surface of the alloy exhibits improved metal dustingcorrosion resistance at high temperatures in carbon-supersaturatedenvironments having relatively low oxygen partial pressures.

In a further exemplary embodiment of the present disclosure, thedisclosed alloy composition comprising an alloy (PQR), and a multi-layeroxide film on the surface of the alloy exhibits the capability ofrapidly forming an outer oxide film to block carbon transfer whilegrowing an adherent inert oxide film slowly to act as a diffusionbarrier to carbon ingress.

In a further exemplary embodiment of the present disclosure, thedisclosed alloy composition comprising an alloy (PQR), and a multi-layeroxide film on the surface of the alloy (PQR) does not poison mostcatalysts used in hydrocarbon conversion processes.

In a further exemplary embodiment of the present disclosure, thedisclosed multi-layer oxide film on the surface of the alloy (PQR) formswhen the alloy is exposed to metal dusting environments with low oxygenpartial pressures.

In a further exemplary embodiment of the present disclosure, thedisclosed multi-layer oxide film on the surface of the alloy (PQR) formsin situ during use of the alloy in a carbon supersaturated environment.

In a further exemplary embodiment of the present disclosure, thedisclosed multi-layer oxide film on the surface of the alloy (PQR) formsprior to use by exposing the alloy to a carbon supersaturatedenvironment.

Another advantage of the alloy compositions comprising an alloy (PQR),and a multi-layer oxide film on the surface of the alloy (PQR) is thatif the protective surface oxide film cracks during use of the alloy in acarbon supersaturated environment, the protective surface oxide filmwill form in the crack to repair the oxide layers thereby protecting thealloy from metal dusting during use.

The disclosed alloy compositions comprising all alloy (PQR), and amulti-layer oxide film on the surface of the alloy have application inapparatus and reactor systems that are in contact with carbonsupersaturated environments at any time during use, including reactors,heat exchangers and process piping.

The disclosed alloy compositions comprising an alloy (PQR), and amulti-layer oxide film on the surface of the alloy may be used toconstruct the surface of apparatus or alternatively coated onto thesurface of apparatus exposed to metal dusting environments.

These and other advantages, features and attributes of the alloycompositions comprising an alloy (PQR), and a multi-layer oxide film onthe surface of the alloy of the present disclosure and theiradvantageous applications and/or uses will be apparent from the detaileddescription which follows, particularly when read in conjunction withthe figures appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist those of ordinary skill in the relevant art in making andusing the subject matter hereof, reference is made to the appendeddrawings, wherein:

FIG. 1 depicts a schematic illustration of the cross sectional structureof protective surface oxide films using aluminum in the alloying metalaccording to this invention.

FIG. 2 depicts a schematic illustration of the cross sectional structureof protective surface oxide films using silicon in the alloying metalaccording to this invention.

FIG. 3 depicts surface and cross sectional scanning electron microscopy(SEM) images showing a M₃O₄/Al₂O₃ surface oxide film, wherein M ispredominantly Mn, but further comprises Cr, Al and Fe, after reactingEM-38 alloy at 650° C. for 160 hours in 50CO-50H₂.

FIG. 4 depicts surface and cross sectional scanning electron microscopy(SEM) images showing a M₃O₄/MM′₂O₄/Al₂O₃ surface oxide film, wherein Mis predominantly Mn, but further comprises of Cr, Al and Fe and M′ ispredominantly Al, but further comprises Cr, Fe and Mn, after reactingEM-38 alloy at 950° C. for 160 hours in 50CO-50H₂.

FIG. 5 depicts (a) scanning electron microscopy (SEM) image showing atwo-layered MnO/MnCr₂O₄ structure and (b) transmission electronmicroscopy (TEM) image revealing further details of a continuousamorphous silica sub-layer after reaction at 650° C. for 160 hours in50CO-50H₂.

FIG. 6 depicts a SEM image showing a complex layered structurecomprising an inner SiO₂/Mn₂SiO₄ layer and an outer Cr₂O₃/MnCr₂O₄ duplexlayer after reaction at 950° C. for 160 hours in 50CO-50H₂.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes alloy compositions of matter which areresistant to metal dusting and comprise (a) an alloy composition that iscapable of forming a protective surface oxide film on its surface whenexposed to a carbon supersaturated environment, and (b) a protectivesurface oxide film on the alloy surface. The alloy compositions of thepresent disclosure offer significant advantages relative to prior artalloy compositions for use as protective coatings to metal dusting onmetal surfaces exposed to carbon supersaturated environments. The alloycompositions of the present disclosure are distinguishable from theprior art in comprising an alloying metal comprising Cr, Mn, and eitherAl, Si or a combination of Al and Si at concentration in an alloy whichforms in situ during use a multi-layer oxide film comprising at leastthree oxide layers when exposed to a carbon supersaturated metal dustingenvironment with low oxygen partial pressures. The advantageousproperties and/or characteristics of the disclosed alloy compositionsare based, at least in part, on the structure of the multi-layer oxidefilm formed on the surface of the alloy composition, which include,inter alia, improved metal dusting corrosion resistance, decreasedpropensity to poison catalysts used in hydrocarbon conversion processes,and improved ease of formation prior to and in use when exposed to acarbon supersaturated environment.

An alloy composition that is capable of forming a protective surfaceoxide film on its surface is represented by the formula (PQR). In thealloy composition (PQR), P is the base metal selected from the groupconsisting of Fe, Ni, Co and mixtures thereof. In the alloy composition,the alloying metal Q comprises Cr, Mn, and either Al, Si, or acombination of Al and Si. The alloying element R comprises at least oneelement selected from the group consisting of B, C, N, Al, Si, P, Ga,Ge, As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru,Rh, Ir, Pd, Pt, Cu, Ag and Au. The alloy metal Q and alloying element Rprovide for enhanced metal dusting corrosion resistance. As anon-limiting example, alloying elements R, such as Sc, La, Y and Ce,provide improved adhesion of in-situ formed surface oxide films, whichcontributes to enhance spalling resistance. Alloying elements R, such asGa, Ge, As, In, Sn, Sb, Pb, Pd, Pt, Cu, Ag and Au, provide reducedcarbon deposition because these elements are non-catalytic to surfacecarbon transfer reaction.

Three preferred embodiments of the alloy compositions disclosed hereinare described in further detail below, and comprise alloying metals (Q)comprising either: (1) Cr, Mn, and Al, (2) Cr, Mn, and Si, or (3) Cr,Mn, Al, and Si.

Alloy Compositions With Alloying Metals Including Aluminum

In the alloy composition (PQR), the base metal P is at least 40 wt %,preferably at least 50 wt %, and more preferably at least 60 wt % basedon the total weight of the alloy. Within the alloying metal Q, theamount of Cr is at least 10 wt %, preferably at least 15 wt %, and morepreferably at least 20 wt %. The amount of Mn is at least 2.5 wt %,preferably at least 5.0 wt %, and more preferably at least 7.5 wt %, andthe amount of Al is at least 2.0 wt %, preferably at least 3.0 wt %, andmore preferably at least 4.0 wt % based on the total weight of thealloy. In one preferred embodiment, the combined amount of the alloyingmetal Q is at least 20 wt %, preferably at least 30 wt %, and morepreferably at least 40 wt % based on the total weight of the alloy. Inthe alloy composition (PQR), the alloying element R is about 0.01 wt %to about 5.0 wt %, preferably about 0.1 wt % to about 5.0 wt %, and morepreferably about 1.0 wt % to about 5.0 wt % based on the total weight ofthe alloy. It is preferred to use an alloying metal Q that providesenhanced metal dusting resistance of the alloy. One example of such analloying metal includes Mn and Al at a mass ratio of Mn to Al of about 1to 2. Along with Cr, this mass ratio of Mn to Al promotes formationin-situ of a MnAl₂O₄ layer within the protective surface oxide film.

When the alloying metal Q includes Al, a suitable class of the alloys ofthe present invention comprise at least 40 wt % of the base metal Pselected from the group consisting of Fe, Ni, Co and mixtures thereof.The alloying metal Q includes at least 10 wt % Cr, at least 2.5 wt % Mn,and at least 2.0 wt % of Al, wherein the total amount of Cr, Mn and Alis at least 20 wt % of the alloy. In addition the alloying element R isabout 0.01 wt % to about 5.0 wt % of the alloy and comprises at leastone clement selected from the group consisting of B, C, N, Si, P, Ga,Ge, As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru,Rh, Ir, Pd, Pt, Cu, Ag and Au. Non-limiting examples of such alloys aregiven in Tahle 1 below. Table 1 is a list of advanced metal dustingresistant alloys capable of forming a manganese aluminate surface oxidefilm.

TABLE 1 Wt. % of Q Alloy Name Alloy Compositions (Weight %) (Cr + Mn +Al) EM-10 Bal.Fe:20.0Cr:2.3Mn:4.5Al:0.5Y:0.3C 26.8 EM-11Bal.Fe:23.5Cr:3.0Mn:6.0Al:0.08C 32.5 EM-20Bal.Fe:10.0Ni:18.0Cr:2.5Mn:5.0Al:0.05C 25.5 EM-21Bal.Fe:21.0Ni:25.0Cr:6.0Mn:3.0Al:0.25C 34.0 EM-22Bal.Fe:33.0Ni:21.0Cr:5.0Mn:4.0Al:0.5Si:0.5Ti:0.07C 30.0 EM-23Bal.Fe:44.0Ni:32.0Cr:5.0Mn:3.0Al:0.9Nb:0.1Ti:0.4C 40.0 EM-30Bal.Ni:14.0Fe:16.0Cr:10.0Mn:5.0Al:0.1C 31.0 EM-31Bal.Ni:8.0Fe:18.0Cr:8.0Mn:4.0Al:0.1C 30.0 EM-32Bal.Ni:3.0Fe:21.0Cr:5.0Mn:3.0Al:0.5Zr:0.5Y:0.2C 29.0 EM-33Bal.Ni:9Fe:28.0Cr:2.5Mn:3.5Al:1.0Si:0.5Y:0.05C 34.0 EM-34Bal.Ni:20.0Cr:5.0Mn:5.0Al:0.05C 30.0 EM-35Bal.Ni:25.0Cr:4.0Mn:4.0Al:0.05C 33.0 EM-36Bal.Fe:10.0Cr:15.0Mn:5.0Al:0.04C 30.0 EM-37Bal.Fe:15.0Cr:15.0Mn:5.0Al:0.04C 35.0 EM-38Bal.Fe:20.0Cr:15.0Mn:5.0Al:0.04C 40.0

A protective surface oxide film comprising at least two layers on thealloy surface, and more preferably three layers forming on the alloysurface. The protective surface oxide film is formed when the alloy isexposed to metal dusting environments with low oxygen partial pressures.An exemplary cross sectional structure of a three-layer protectivesurface oxide film according to present invention is illustrated in FIG.1.

The outer layer, also referred to as the first oxide layer (the layercontacting the carbon supersaturated environment or furthest away fromthe alloy) is made up of a thermodynamically stable oxide, which canrapidly cover up the alloy surface and block carbon entry into thealloy. The composition of the first oxide layer is dependent on thecomposition of the alloy from which it is formed. The first oxide layeris an oxide selected from the group consisting of a manganese oxide(MO), and manganese chromate (M₃O₄), a chromium oxide (M₂O₃) andmixtures thereof, wherein M is predominantly Mn and may further compriseelements of the base metal P, the alloying metal, Q and the alloyingelement R.

Beneath the first oxide layer, a second layer forms (herein referred toas the second oxide layer) either simultaneously with or following thefirst oxide layer formation. The second oxide layer is the mostthermodynamically stable oxide film, which is established beneath thefirst oxide layer and adherent to the first oxide layer. A non-limitingexample of the second oxide layer is an aluminum oxide (Al₂O₃). Thecomposition of the second oxide layer is dependent on the composition ofthe alloy from which it is formed. It can be described in general asM₂O₃, wherein M is predominantly Al and may further comprise elements ofthe base metal P, the alloying metal, Q and the alloying element R.

Between the first oxide layer and the second oxide layer, a third layerforms (herein referred to as the third oxide layer) eithersimultaneously with or following the second oxide layer formation. Thethird oxide layer is an oxide film which is established by the reactionbetween the first oxide layer and the second oxide layer. As thereaction progresses, both the first oxide layer and the second oxidelayer may be used up. In this case, the third oxide layer provides longterm resistance for metal dusting corrosion. A non-limiting example ofthe third oxide layer is manganese aluminum oxide (MnAl₂O₄). Thecomposition of the third oxide layer is dependent on the composition ofthe alloy from which it is formed. It can be described in general asMM′₂O₄, wherein M is predominantly Mn and M′ is predominantly Al, butboth M and M′ may further comprise elements of the base metal P, thealloying metal Q, and the alloying element R.

The alloy composition of the present invention is resistant to metaldusting corrosion, and comprises: (a) an alloy and (b) a protectivesurface oxide film on the alloy. The protective surface oxide filmcomprises at least two oxide layers, and preferably three oxide layers.The first oxide layer is an oxide selected from the group consisting ofa manganese-oxide (MO), a manganese chromate (M₃O₄), a chromium oxide(M₂O₃) and mixtures thereof, the second oxide layer is an aluminum oxide(M₂O₃) and the third oxide layer is a manganese aluminum oxide (MM′₂O₄).The alloy comprises the base metal P, the alloying metal Q, and thealloying element R. The metal P is selected from the group consisting ofFe, Ni, Co and mixtures thereof. The alloying metal Q comprises Cr, Mnand Al. The alloying element R comprises at least one element selectedfrom the group consisting of B, C, N, Si, P, Ga, Ge, As, In, Sn, Sb, Pb,Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, Pd, Pt, Cu, Agand Au. The metal P is present in the alloy at a concentration of atleast about 40 wt % based on the total weight of the alloy. The alloyingelement R is present in the alloy at a concentration of about 0.01 wt %to about 5.0 wt % based on the total weight of the alloy. In thealloying metal Q, the Cr is present in the alloy at a concentration ofat least about 10 wt % Cr, the Mn is present in the alloy at aconcentration of at least about 2.5 wt %, and the Al is present in thealloy at a concentration of at least about 2.0 wt %, wherein thecombined amount of Cr, Mn and Al is greater than or equal to 20 wt % ofthe alloy.

The protective surface oxide film may be formed in situ during use ofthe alloy in a carbon supersaturated environment, or prepared byexposing the alloy to a carbon supersaturated environment prior to thealloy's use. A further benefit of the present invention is that if theprotective surface oxide film cracks during use of the alloy in a carbonsupersaturated environment, the protective surface oxide film will formin the crack to repair the oxide layers, thereby protecting the alloyfrom metal dusting during use.

A method for preventing metal dusting of metal surfaces exposed tocarbon supersaturated environments is disclosed in the presentinvention. The method for preventing metal dusting comprises the stepsof constructing the metal surface of, coextruding a metal dustingresistant alloy composition (PQR) onto a conventional steel or nickelbase alloy, or coating the metal surfaces with a metal dusting resistantalloy composition (PQR). The metal P is selected from the groupconsisting of Fe, Ni, Co and mixtures thereof. The alloying metal Qcomprises Cr, Mn, and Al. The alloying metal R comprises at least oneelement selected from the group consisting of B, C, N, Si, P, Ga, Ge,As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh,Ir, Pd, Pt, Cu, Ag and Au. The metal P is present in the alloy at aconcentration of at least about 40 wt % based on the total weight of thealloy. The alloying element R is present in the alloy at a concentrationof about 0.01 wt % to about 5.0 wt % based on the total weight of thealloy. In the alloying metal Q, the Cr is present in the alloy at aconcentration of at least about 10 wt % Cr, the Mn at a concentration ofat least about 2.5 wt %, and the Al at a concentration of at least about2.0 wt %, wherein the combined amount of Cr, Mn and Al is greater thanor equal to 20 wt %.

Metal surfaces may be constructed of the alloy, coextruded with thealloy, coated with the alloy, or a combination of the three. Theprotective surface oxide films described above will be formed in situduring operation of the unit in a carbon supersaturated environment. Thepresent invention further comprises a protective surface oxide coatingcomprising at least two oxide layers, and preferably three oxide layers,wherein the first oxide layer is an oxide selected from the groupconsisting of a manganese oxide (MO), a manganese chromate (M₃O₄), achromium oxide (M₂O₃) and mixtures thereof, the second oxide layer is analuminum oxide (M₂O₃) and the third oxide layer is a manganese aluminumoxide (MM′₂O₄). The first oxide layer is the layer located furthest awayfrom the alloy, and the second oxide layer is the layer located adjacentto the alloy surface.

Alloy Compositions With Alloying Metals Including Silicon

In the alloy composition (PQR), the base metal P is at least 40 wt %,preferably at least 50 wt %, and more preferably at least 60 wt % basedon the total weight of the alloy. Within the alloying metal Q, theamount of Cr is at least 10 wt %, preferably at least 15 wt %, and morepreferably at least 20 wt %. The amount of Mn is at least 6.0 wt %, andpreferably at least 8.0 wt %, and the amount of Si is at least 2.0 wt %,preferably at least 3.0 wt %, and more preferably at least 4.0 wt %based on the total weight of the alloy. In one preferred embodiment, thecombined amount of the alloying metal Q is at least 20 wt %, preferablyat least 25 wt %, and more preferably at least 30 wt % based on thetotal weight of the alloy. In the alloy composition (PQR), the alloyingelement R is about 0.01 wt % to about 5.0 wt %, preferably about 0.1 wt% to about 5.0 wt %, and more preferably about 1.0 wt % to about 5.0 wt% based on the total weight of the alloy. It is preferred to use analloying metal Q that provides enhanced metal dusting resistance of thealloy. One example of such an alloying metal includes Mn and Si at amass ratio of Mn to Si of about 2 to 1. Along with Cr, this mass ratioof Mn to Si promotes formation in-situ of a Mn₂SiO₄ layer within theprotective surface oxide film.

When the alloying metal Q includes Si, a suitable class of the alloys ofthe present invention comprise at least 40 wt % of the base metal Pselected from the group consisting of Fe, Ni, Co and mixtures thereof.The alloying metal Q includes at least 10 wt % Cr, at least 6.0 wt % Mn,and at least 2.0 wt % of Si, wherein the total amount of Cr, Mn and Siis at least 20 wt % of the alloy. In addition the alloying element R isabout 0.01 wt % to about 5.0 wt % of the alloy and comprises at leastone element selected from the group consisting of B, C, N, Al, P, Ga,Ge, As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru,Rh, Ir, Pd, Pt, Cu, Ag and Au. Non-limiting examples of such alloys aregiven in Table 2 below. Table 2 is a list of advanced metal dustingresistant alloys capable of forming a manganese silicate surface oxidefilm.

TABLE 2 Wt. % of Q Alloy Name Alloy Compositions (Weight %) (Cr + Mn +Si) EM-100 Bal.Fe:20.0Cr:4.0Mn:2.0Si:0.5Y:0.3C 26.0 EM-101Bal.Fe:23.5Cr:6.0Mn:3.0Si:0.08C 32.5 EM-200Bal.Fe:8.2Ni:16.4Cr:8.1Mn:4.0Si:0.1C:0.1N 28.5 EM-201Bal.Fe:10.0Ni:20.0Cr:8.0Mn:4.0Si:0.05C 32.0 EM-202Bal.Fe:21.0Ni:25.0Cr:6.0Mn:3.0Si:0.25C 34.0 EM-203Bal.Fe:33.0Ni:21.0Cr:7.0Mn:3.5Si:0.5Al:0.5Ti:0.07C 31.5 EM-204Bal.Fe:44.0Ni:32.0Cr:4.0Mn:2.0Si:0.9Nb:0.1Ti:0.4C 38.0 EM-300Bal.Ni:8.0Fe:16.0Cr:8.0Mn:4.0Si:0.1C 28.0 EM-301Bal.Ni:3.0Fe:21.0Cr:4.0Mn:2.0Si:0.5Zr:0.5Y:0.2C 27.0 EM-302Bal.Ni:20.0Cr:6.0Mn:3.0Si:1.0Al:0.5Y:0.05C 29.0

A protective surface oxide film comprises at least three layers on thealloy surface, and more preferably four layers on the alloy surface. Theprotective film is formed when the alloy is exposed to metal dustingenvironments with low oxygen partial pressures. An exemplary crosssectional structure of a four-layer protective surface oxide filmaccording to the present invention is illustrated in FIG. 2.

The outer layer, also referred to as the first oxide layer (the layercontacting the carbon supersaturated environment or furthest away fromthe alloy) is made up of a thermodynamically stable oxide, which callrapidly cover up the alloy surface and block carbon entry into thealloy. The first oxide layer is a thermodynamically stable manganeseoxide (MnO), which forms faster than the carbon in the supersaturatedenvironment, and is able to penetrate the surface of the alloy. Themanganese oxide is referred to as a fast forming layer. The compositionof the first oxide layer is dependent on the composition of the alloyfrom which it is formed. It can be described in general as MO, wherein Mis predominantly Mn, and may further comprise elements of the base metalP, the alloying metal Q, and the alloying element R.

Beneath the manganese oxide layer, a second layer forms (herein referredto as the second oxide layer) either simultaneously with or followingthe manganese oxide layer formation. The second oxide layer is an oxidefilm, which is established beneath the manganese oxide layer andadherent to the manganese oxide layer. Non-limiting examples of thesecond oxide layer are manganese chromate (MnCr₂O₄) and chromium oxide(Cr₂O₃). The composition of the second oxide layer is dependent on thecomposition of the alloy from which it is formed. It can be described ingeneral as M₃O₄ and M₂O₃, wherein M is predominantly Mn and Cr and mayfurther comprise elements of the base metal P, the alloying metal, Q andthe alloying element R. Thus, the second oxide layer is an oxideselected from the group consisting of a manganese chromate (M₃O₄), achromium oxide (M₂O₃), and mixtures thereof.

Beneath the second oxide layer, a third layer forms (herein referred toas the third oxide layer) either simultaneously with or following thesecond oxide layer formation. The third oxide layer is the mostthermodynamically stable oxide film, which is established beneath thesecond oxide layer and adherent to the second oxide layer. Anon-limiting example of the third oxide layer is silicon oxide (SiO₂).The composition of the third oxide layer is dependent on the compositionof the alloy from which it is formed. It can be described in general asMO₂, wherein M is predominantly Si, and may further comprise elements ofthe base metal P, the alloying metal, Q and the alloying element R.

Between the second oxide layer and the third oxide layer, a fourth layerforms (herein referred to as the fourth oxide layer) eithersimultaneously with or following the third oxide layer formation. Thefourth oxide layer is an oxide film which is established by the reactionbetween the second oxide layer and the third oxide layer. As thereaction progresses, both the second oxide layer and the third oxidelayer may be used up. In this case, the fourth oxide layer provides longterm resistance for metal dusting corrosion. A non-limiting example ofthe fourth oxide layer is manganese silicon oxide (Mn₂SiO₄). Thecomposition of the fourth oxide layer is dependent upon the compositionof the alloy from which it is formed. It can be described in general asM₂M′O₄, wherein M is predominantly Mn and M′ is predominantly Si, butboth M and M′ may further comprise elements of the base metal P, thealloying metal Q, and the alloying element R.

The alloy composition of the present invention is resistant to metaldusting corrosion and comprises: (a) an alloy and (b) a protectivesurface oxide film on the alloy. The protective surface oxide filmcomprises at least three oxide layers, and preferably four oxide layers,wherein the first oxide layer is a manganese oxide (MO), the secondoxide layer is an oxide selected from the group consisting of amanganese chromate (M₃O₄), a chromium oxide (M₂O₃) and mixtures thereof,the third oxide layer is a silicon oxide (MO₂) and the fourth oxidelayer is manganese silicon oxide (M₂M′O₄). The alloy comprises the basemetal P, the alloying metal Q and the alloying element R. The metal P isselected from the group consisting of Fe, Ni, Co and mixtures thereof.The alloying metal Q comprises Cr, Mn, and Si. The alloying element Rcomprises at least one element selected from the group consisting of B,C, N, Al, P, Ga, Ge, As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V,Nb, Ta, Mo, W, Ru, Rh, Ir, Pd, Pt, Cu, Ag, and Au. The metal P ispresent in the alloy at a concentration of at least about 40 wt % basedon the total weight of the alloy. The alloying element R is present inthe alloy at a concentration of about 0.01 wt % to about 5.0 wt % basedon the total weight of the alloy. In the alloying metal Q, the Cr ispresent in the alloy at a concentration of at least about 10 wt %, theMn is present in the alloy at a concentration of at least about 6.0 wt%, and the Si is present in the alloy at a concentration of at leastabout 2.0 wt %, and wherein the combined amount of Cr, Mn and Si isgreater than or equal to 20 wt %.

The protective surface oxide film may be formed in situ during use ofthe alloy in a carbon supersaturated environment, or prepared byexposing the alloy to a carbon supersaturated environment prior to thealloy's use. A further benefit of the present invention is that if theprotective surface oxide film cracks during use of the alloy in a carbonsupersaturated environment, the protective surface oxide film will formin the crack to repair the oxide layers thereby protecting the alloyfrom metal dusting during use.

A method for preventing metal dusting of metal surfaces exposed tocarbon supersaturated environments is also disclosed in the presentinvention. The method for preventing metal dusting comprises the stepsof constructing the metal surface of, coextruding a metal dustingresistant alloy composition (PQR) onto a conventional steel or nickelbase alloy, or coating the metal surfaces with a metal dusting resistantalloy composition (PQR). The base metal P is selected from the groupconsisting of Fe, Ni, Co and mixtures thereof. The alloying metal Qcomprises Cr, Mn and Si. The alloying element R comprises at least oneelement selected from the group consisting of B, C, N, Al, P, Ga, Ge,As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh,Ir, Pd, Pt, Cu, Ag and Au. The metal P is present in the alloy at aconcentration of at least about 40 % based on the total weight of thealloy. The alloying element R is present in the alloy at a concentrationof about 0.01 wt % to about 5.0 wt % based on the total weight of thealloy. In the alloying metal Q, Cr is present in the alloy at aconcentration of at least about 10 wt %, the Mn at a concentration of atleast about 6.0 wt %, and the Si at a concentration of at least about2.0 wt %, wherein the combined amount of Cr, Mn and Si is greater thanor equal to 20 wt %.

The metal surfaces may be constructed of the alloy, coextruded with thealloy, or coated with the alloy and the protective surface oxide filmsdescribed above will be formed in situ during operation of the unit in acarbon supersaturated environment. The present invention furthercomprises a protective surface oxide coating comprising at least threeoxide layers, and preferably four oxide layers, wherein the first oxidelayer is a manganese oxide (MO), the second oxide layer is an oxideselected from the group consisting of a manganese chromate (M₃O₄), achromium oxide (M₂O₃) and mixtures thereof, the third oxide layer is asilicon oxide (MO₂) and the fourth oxide layer is manganese siliconoxide (M₂M′O₄). The first oxide layer is the layer located furthest awayfrom the alloy, and the third oxide layer is located adjacent to thealloy surface.

Alloy Compositions With Alloying Metals Including Aluminum and Silicon

In the alloy composition (PQR), the base metal P is at least 40 wt %,preferably at least 50 wt %, and more preferably at least 60 wt % basedon the total weight of the alloy. Within the alloying metal Q, theamount of Cr is at least 10 wt %, preferably at least 15 wt %, and morepreferably at least 20 wt %. The amount of Mn is at least 2.5 wt %,preferably at least 5.0 wt %, and more preferably at least 7.5 wt %. Theamount of Al is at least 2.0 wt %, preferably at least 3.0 wt %, andmore preferably at least 4.0 wt %. The amount of Si is at least 2.0 wt%, preferably at least 3.0 wt %, and more preferably at least 4.0 wt %based on the total weight of the alloy. In one preferred embodiment, thecombined amount of the alloying metal Q is at least 20 wt %, preferablyat least 25 wt %, and more preferably at least 30 wt % based on thetotal weight of the alloy. In the alloy composition (PQR), the alloyingelement R is about 0.01 wt % to about 5.0 wt %, preferably about 0.1 wt% to about 5.0 wt %, and more preferably about 1.0 wt % to about 5.0 wt% based on the total weight of the alloy.

When the alloying metal Q includes Al and Si, a suitable class of thealloys of the present invention comprise at least 40 wt % of the basemetal P selected from the group consisting of Fe, Ni, Co and mixturesthereof. The alloying metal Q includes at least 10 wt % Cr, at least 2.5wt % Mn, at least 2.0 wt % Al, and at least 2.0 wt % of Si, wherein thetotal amount of Cr, Mn, Al and Si is at least 20 wt % of the alloy. Inaddition the alloying element R is about 0.01 wt % to about 5.0 wt % ofthe alloy and comprises at least one element selected from the groupconsisting of B, C, N, P, Ga, Ge, As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti,Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, Pd, Pt, Cu, Ag and Au.

A protective surface oxide film comprises at least two layers on thealloy surface, and more preferably three layers on the alloy surface.The outer layer, also referred to as the first oxide layer (the layercontacting the carbon supersaturated environment or furthest away fromthe alloy) is made up of a thermodynamically stable oxide, which canrapidly cover up the alloy surface and block carbon entry into thealloy. The composition of the first oxide layer is dependent on thecomposition of the alloy from which it is formed. The first oxide layeris an oxide selected from the group consisting of a manganese oxide(MO), a manganese chromate (M₃O₄), a chromium oxide (M₂O₃) and mixturesthereof, wherein M is predominantly Mn and may further comprise elementsof the base metal P, the alloying metal, Q and the alloying element R.

Beneath the first oxide layer, a second layer forms (herein referred toas the second oxide layer) either simultaneously with or following thefirst oxide layer formation. The second oxide layer is the mostthermodynamically stable oxide film, which is established beneath thefirst oxide layer and adherent to the first oxide layer. A non-limitingexample of the second oxide layer is an aluminum oxide (Al₂O₃), asilicon oxide (SiO₂), and a solid solution of both aluminum oxide andsilicon oxide (e.g. mullite, 3Al₂O₃-2SiO₂). The composition of thesecond oxide layer is dependent on the composition of the alloy fromwhich it is formed. It can be described in general as M_(x)O_(y),wherein M is predominantly Al and Si and may further comprise elementsof the base metal P, the alloying metal, Q and the alloying element R.

Between the first oxide layer and the second oxide layer, a third layerforms (herein referred to as the third oxide layer) eithersimultaneously with or following the second oxide layer formation. Thethird oxide layer is an oxide film which is established by the reactionbetween the first oxide layer and the second oxide layer. As thereaction progresses, both the first oxide layer and the second oxidelayer may be used up. In this case, the third oxide layer provides longterm resistance for metal dusting corrosion. A non-limiting example ofthe third oxide layer is manganese aluminum oxide (MnAl₂O₄) andmanganese silicon oxide (Mn₂SiO₄). The composition of the third oxidelayer is dependent on the composition of the alloy from which it isformed. It can be described in general as M_(x)M′_(y)O₄ wherein M ispredominantly Mn and M′ is predominantly Al and Si, but both M and M′may further comprise elements of the base metal P, the alloying metal Q,and the alloying element R.

The alloy composition of the present invention is resistant to metaldusting corrosion and comprises: (a) an alloy and (b) a protectivesurface oxide film on the alloy. The protective surface oxide filmcomprises at least two oxide layers, and preferably three oxide layers,wherein a first oxide layer comprises an oxide selected from the groupconsisting of a manganese oxide, a manganese chromate, a chromium oxide,and mixtures thereof, and is an outer layer located adjacent to a thirdoxide layer, a second oxide layer comprises aluminum oxide, siliconoxide, a solid solution of aluminum oxide and silicon oxide, andmixtures thereof, and is located between the surface of said alloy (PQR)and said third oxide layer, and said third oxide layer comprisesmanganese aluminum oxide, manganese silicon oxide, and mixtures thereof,and is located between said first oxide layer and said second oxidelayer.

The alloy comprises the base metal P, the alloying metal Q and thealloying element R. The metal P is selected from the group consisting ofFe, Ni, Co and mixtures thereof. The alloying metal Q comprises Cr, Mn,Al, and Si. The alloying element R comprises at least one elementselected from the group consisting of B, C, N, P, Ga, Ge, As, In, Sn,Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, Pd, Pt,Cu, Ag and Au. The metal P is present in the alloy at a concentration ofat least about 40 wt % based on the total weight of the alloy. Thealloying element R is present in the alloy at a concentration of about0.01 wt % to about 5.0 wt % based on the total weight of the alloy. Inthe alloying metal Q, the Cr is present in the alloy at a concentrationof at least about 10 wt %, the Mn is present in the alloy at aconcentration of at least about 2.5 wt %, the Al is present in the alloyat a concentration of at least about 2.0 wt %, and the Si is present inthe alloy at a concentration of at least about 2.0 wt %, and wherein thecombined amount of Cr, Mn, Al and Si is greater than or equal to 20 wt%.

The protective surface oxide film may he formed in situ during use ofthe alloy in a carbon supersaturated environment, or prepared byexposing the alloy to a carbon supersaturated environment prior to thealloy's use. A further benefit of the present invention is that if theprotective surface oxide film cracks during use of the alloy in a carbonsupersaturated environment, the protective surface oxide film will formin the crack to repair the oxide layers thereby protecting the alloyfrom metal dusting during use.

A method for preventing metal dusting of metal surfaces exposed tocarbon supersaturated environments is also disclosed in the presentinvention. The method for preventing metal dusting comprises the stepsof constructing the metal surface of, coextruding a metal dustingresistant alloy composition (PQR) onto a conventional steel or nickelbase alloy, or coating the metal surfaces with a metal dusting resistantalloy composition (PQR). The metal dusting resistant alloy composition(PQR) comprises the base metal P, the alloying metal Q, and the alloyingelement R. The base metal P is selected from the group consisting of Fe,Ni, Co and mixtures thereof. The alloying metal Q comprises Cr, Mn, Aland Si. The alloying element R comprises at least one element selectedfrom the group consisting of B, C, N, P, Ga, Ge, As, In, Sn, Sb, Pb, Sc,La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, Pd, Pt, Cu, Ag andAu. The metal P is present in the alloy at a concentration of at leastabout 40 wt % based on the total weight of the alloy. The alloyingelement R is present in the alloy at a concentration of about 0.01 wt %to about 5.0 wt % based on the total weight of the alloy. In thealloying metal Q, Cr is present in the alloy at a concentration of atleast about 10 wt %, the Mn at a concentration of at least about 2.5 wt%, the Al at a concentration of at least about 2.0 wt %, and the Si at aconcentration of at least about 2.0 wt %, w herein the combined amountof Cr, Mn and Si is greater than or equal to 20 wt %. The metal surfacesmay be constructed of the alloy, coextrtided with the alloy or coatedwith the alloy, and the protective surface oxide films described abovewill be formed in situ during operation of the unit in a carbonsupersaturated environment.

Uses of Alloy Compositions and Methods of Application

Alloys of the multi-layer compositions described herein may be utilizedto construct the surface of apparatus exposed to metal dustingenvironments. Alternatively, alloys of the multi-layer compositions ofthe instant invention may be coextruded with a conventional steel ornickel base alloy using steel coextrusion techniques known to oneskilled in the art. The coextruded structure may comprise two or morelayers, wherein an outer layer comprises the alloy composition of thepresent invention. Additionally, the existing surfaces of apparatussusceptible to metal dusting may be coated with the alloys of themulti-layer compositions of the instant invention using coatingtechniques known to one skilled in the art. Exemplary coating techniquessuitable for coating metals with the alloy compositions described hereininclude, but are not limited to, thermal spraying, plasma deposition,chemical vapor deposition, and sputtering. Therefore, refinery apparatusmay be either constructed of, coextruded with, or coated with alloys ofthe multi-layer compositions described herein, and the protectivesurface oxide films formed during use of the apparatus, or formed priorto use of the apparatus.

When utilized as coatings on existing surfaces, the coating thicknessmay range from about 10 to about 200 microns, and preferably from about50 to about 100 microns.

Surfaces which would benefit from the alloy compositions of the instantinvention include apparatus and reactor systems that are in contact withcarbon supersaturated environments at any time during use. Theseapparatus and reactor systems include, but are not limited to, reactors,heat exchangers, and process piping.

The protective coatings or films on the surface of the alloys describedherein are formed on the alloy surface by exposing the alloy to a metaldusting environment such as a 50CO:50H₂ mixture. Therefore, theprotective coatings may be formed during use or prior to use of thealloys under reaction conditions in which they are exposed to metaldusting environments. The preferred temperature range is from about 350°C. to about 1050° C., preferably from about 550° C. to about 1050° C.Typical exposure times can range from about 1 hour to about 200 hours,preferably from about 1 hour to about 100 hours.

Applicants have attempted to disclose all embodiments and applicationsof the disclosed subject matter that could be reasonably foreseen.However, there may be unforeseeable, insubstantial modifications thatremain as equivalents. While the present invention has been described inconjunction with specific, exemplary embodiments thereof, it is evidentthat many alterations, modifications, and variations will be apparent tothose skilled in the art in light of the foregoing description withoutdeparting from the spirit or scope of the present disclosure.Accordingly, the present disclosure is intended to embrace all suchalterations, modifications, and variations of the above detaileddescription.

The following examples illustrate the present invention and theadvantages thereto without limiting the scope thereof.

Test Methods

The determination of weight percent of elements in the surface oxidefilms and the alloys was determined by standard EDXS analyses. Forcommercially available alloys, rectangular samples of 0.5 inch×0.25inch×0.06 inch were prepared from the alloy sheets. High performancealloys with superior metal dusting resistance (EM-36, EM-37 and EM-38)containing different concentrations of Fe, Cr, and Al were prepared byarc melting. The arc melted alloys were rolled into thin sheets of about⅛ inch thickness. The sheets were annealed at 1100° C. overnight ininert argon atmosphere and furnace-cooled to room temperature.Rectangular samples of 0.5 inch×0.25 inch were cut from the sheets. Thesample faces were polished to either 600 grit finish or Linde B (0.05micrometers alumina powder) finish and cleaned in acetone. The corrosionkinetics of various alloy specimens were investigated by exposing thespecimens to a 50CO-50H₂ (vol. %) environment for 160 hours at testtemperatures ranging from 550° C. to 950° C. A Cahn 1000 electrobalancewas used to measure the carbon pick up of the specimen. Carbon pick upis an indication of metal dusting corrosion. A cross section of thesurface of the specimen also was examined using an SEM.

EXAMPLES Illustrative Examples of Alloy Compositions Using Aluminum inthe Alloying Metal

Table 3 below is a list of the alloys used in these experiments.

TABLE 3 Wt. % of Q Alloy UNS No. Alloy Compositions (Weight %) (Cr +Mn + Al) Inconel 600 N06600 Bal.Ni:8.0Fe:15.5Cr:0.5Mn:0.3Si:0.1C N/AKHR-45A⁽¹⁾ N/A Bal.Fe:43.6Ni:32.1Cr:1.0Mn:1.7Si:0.9Nb: N/A 0.1Ti:0.4CIncoloy 800H N08810 Bal.Fe:33.0Ni:21.0Cr:0.8Mn:0.5Al:0.4Si: 22.30.5Ti:0.07C Inconel 601 N06601 Bal.Ni:14.4Fe:23.0Cr:0.3Mn:1.4Al:0.5Si:24.7 0.1C Haynes 214 N07214 Bal.Ni:3.0Fe:2.0Co:16.0Cr:0.5Mn:4.5Al: 21.00.2Si:0.5Mo:0.5Ti:0.05C EM-36 Bal.Fe:10.0Cr:15.0Mn:5.0Al:0.04C 30.0EM-37 Bal.Fe:15.0Cr:15.0Mn:5.0Al:0.04C 35.0 EM-38Bal.Fe:20.0Cr:15.0Mn:5.0Al:0.04C 40.0 ⁽¹⁾KHR-45A: 35/45carburization-resistant alloy (Kubota Metal Corporation).

Following the test method described above, samples of the followingalloys were tested: Inconel 600, KHR-45A, Incoloy 800H, Hayenes 214,EM-36, EM-37 and EM-38. The results of the gravimetric measurements areshown in Table 4. Table 4 depicts the mass gain due to carbon deposition(a measure of metal dusting corrosion) on Linde B finished alloys afterreaction at 650° C. in 50CO-50H₂ gas mixture for 160 hours.

TABLE 4 Wt. % Wt. % Wt. % Wt % of Q Mass Gain Alloy Cr Mn Al (Cr + Mn +Al) (mg/cm²) Inconel 600 15.5 0.5 N/A 60.0~65.0 KHR-45A 32.1 1.0 N/A140.0~160.0 Incoloy 21.0 0.8 0.5 22.3 180.0~200.0 800H Haynes 214 16.00.5 4.5 21.0 85.0~95.0 EM-36 10.0 15.0 5.0 30.0 0.6 EM-37 15.0 15.0 5.035.0 0.5 EM-38 20.0 15.0 5.0 40.0 0.4

After reaction of EM-38 alloy at 650° C. for 160 hours in 50CO-50H₂, theoxide films are made up of outer M₃O₄ and inner amorphous Al₂O₃ layers.Surface and cross-sectional SEM images in FIG. 3 reveal a M₃O₄/Al₂O₃surface oxide film wherein M is predominantly Mn but further comprisesof Cr, Al and Fe. Thus the two oxide layers formed according to theinstant invention provide metal dusting corrosion resistance to thealloy.

EM-38 alloy was tested at a higher temperature of 950° C. for 160 hoursin 50CO-50H₂. A more complex layered structure is developed tocomprising an inner MM′₂O₄/Al₂O₃ layer and an outer M₃O₄ layer, whereinM is predominantly Mn, but further comprises of Cr, Al and Fe. M′ ispredominantly Al, but further comprises of Cr, Fe and Mn. This isexhibited in FIG. 4, surface SEM images, and cross-sectional SEM images.Thus three oxide layers formed according to the instant inventionprovide metal dusting corrosion resistance to the alloy.

Selected alloys (Incoloy 800H, Inconel 601, Haynes 214, EM-36, EM-37 andEM-38) were also tested for metal dusting by exposing the specimens to a50CO-50H₂ gaseous environment at 550° C. for up to 160 hours. Aftermetal dusting exposure, the sample surface was covered with carbon,which always accompanies metal dusting corrosion. Susceptibility ofmetal dusting corrosion was investigated by optical microscopy andcross-sectional SEM examination of the corrosion surface. The averagediameter and number of corrosion pits observed on the surface are usedas measures of metal dusting corrosion. These results are summarized inTable 5, which shows the diameter of pits (μm) and number of pits/unitarea (25 mm²) on Linde B finished alloys after reaction at 550° C. in50CO-50H₂ gas mixture for 160 hrs.

TABLE 5 Diameter Wt. Wt. % Wt. Wt % of Q of Pits Number of Alloy % Cr Mn% Al (Cr + Mn + Al) (μm) Pits per 25 mm² Incoloy 800H 21.0 0.8 0.5 22.3400  135 Inconel 601 23.0 0.3 1.4 24.7 30  20 Haynes 214 16.0 0.5 4.521.0 50 550 EM-36 10.0 15.0 5.0 30.0 No Pits No Pits EM-37 15.0 15.0 5.035.0 No Pits No Pits EM-38 20.0 15.0 5.0 40.0 No Pits No Pits

All alloys except EM-36, EM-37 and EM-38 suffered extensive metaldusting attack as shown in Table 5. Metal dusting resistance of EMalloys is attributed to combined Cr, Mn and Al addition into the alloy,and subsequent surface oxide film formation as described in the presentinvention.

Illustrative Examples of Alloy Compositions Using Silicon as theAlloying Metal

Table 6 below is list of the alloys used in these experiments.

TABLE 6 Wt. % of Q Alloy UNS No. Alloy Compositions (Weight %) (Cr +Mn + Si) 304SS S30400 Bal.Fe:8.2Ni:18.2Cr:1.4Mn:0.5Si:0.06C 20.1 310SSS31000 Bal.Fe:21.0Ni:25.0Cr:2.0Mn:1.5Si:0.25C 28.5 Incoloy 800H N08810Bal.Fe:33.0Ni:21.0Cr:0.8Mn:0.4Si:0.5Al:0.5Ti: 22.2 0.07C Inconel 600N06600 Bal.Ni:8.0Fe:15.5Cr:0.5Mn:0.3Si:0.1C 16.3 KHR-45A⁽¹⁾ N/ABal.Fe:43.6Ni:32.1Cr:1.0Mn:1.7Si:0.9Nb: 34.8 0.1Ti:0.4C EM-200Bal.Fe:8.2Ni:16.4Cr:8.1Mn:4.0Si:0.1C:0.1N 28.5 ⁽¹⁾KHR-45A: 35/45carburization-resistant alloy (Kubota Metal Corporation).

Following the procedure described above, samples of the following alloyswere tested: Inconel 600, KHR-45A and EM-200. The results of thegravimetric measurements are shown in Table 7, which depicts the massgain due to carbon deposition (a measure of metal dusting corrosion) onLinde B finished alloys after reaction at 650° C. in a 50CO-50H₂ gasmixture for 160 hours.

TABLE 7 Wt. % Wt. % Wt. % Wt % of Q Mass Gain Alloy Cr Mn Si (Cr + Mn +Si) (mg/cm²) Inconel 600 15.5 0.5 0.3 16.3 60.0~65.0 KHR-45A 32.1 1.01.7 34.8 140.0~160.0 EM-200 16.4 8.1 4.0 28.5 0.0

After reaction of EM-200 alloy at 650° C. for 160 hours in 50CO-50H₂,the oxide films are made up of outer MnO layer and an inner MnCr₂O₄layer with a continuous amorphous silica sub-layer. A cross-sectionalSEM image in FIG. 5 a reveals a two-layered MnO/MnCr₂O₄ structure. FIG.5 b, a bright field TEM image, shows an amorphous silica sub-layer atthe oxide/alloy interface. Thus three oxide layers formed according tothis instant invention provide metal dusting corrosion resistance of thealloy.

EM-200 alloy was tested at a higher temperature of 950° C. for 160 hoursin 50CO-50H₂. A more complex layered structure is developed comprisingan inner SiO₂/Mn₂SiO₄ layer and an outer Cr₂O₃/MnCr₂O₄ duplex layer withMnO crystals on the surface. This is shown in FIG. 6, which is a crosssectional SEM image. Thus three oxide layers formed according to thisinstant invention provide metal dusting corrosion resistance to thealloy.

Selected alloys (304SS, 310SS, Incoloy 800H, Inconel 600, KHR-45A andEM-200) were also tested for metal dusting by exposing the specimens toa 50CO-50H₂ gaseous environment at 550° C. for up to 160 hours. Aftermetal dusting exposure, the sample surface was covered with carbon,which always accompanies metal dusting corrosion. Susceptibility ofmetal dusting corrosion was investigated by optical microscopy andcross-sectional SEM examination of the corrosion surface. The averagediameter and number of corrosion pits observed on the surface are usedas measures of metal dusting corrosion. These results are summarized inTable 8, which depicts the diameter of pits (μm) and number of pits/unitarea (25 mm²) on Linde B finished alloys after reaction at 550° C. in50CO-50H₂ gas mixture for 160 hrs.

TABLE 8 Wt. % Wt. % Wt. % Wt % of Q Diameter of Number of Pits Alloy CrMn Si (Cr + Mn + Si) Pits (μm) per 25 mm² 304SS 18.2 1.4 0.5 20.1 310260 310SS 25.0 2.0 1.5 28.5 80 5 Incoloy 800H 21.0 0.8 0.4 22.2 400 135Inconel 600 15.5 0.5 0.3 16.3 70 750 KHR-45A 32.1 1.0 1.7 34.8 90 320EM-200 16.4 8.1 4.0 28.5 No Pits No Pits

All alloys except EM-200 suffered extensive metal dusting attack asshown in Table 8. Metal dusting resistance of EM-200 alloy is attributedto combined Cr, Mn and Si addition into the alloy, and subsequentsurface oxide film formation as described in the present invention.

1-54. (canceled)
 55. The method of preventing metal dusting of claim 54,wherein said alloy composition is from about 10 to about 200 microns inthickness.
 56. The method of preventing metal dusting of claim 48,wherein said multi-layer oxide film is formed in situ during use of saidalloy composition in a carbon supersaturated metal dusting environment.57. The method of preventing metal dusting of claim 48, wherein saidalloy composition comprises the inner surface of refinery apparatus andreactor systems exposed to a carbon supersaturated environment.
 58. Analloy composition comprising an alloy (PQR), wherein P is a metalselected from the group consisting of Fe, Ni, Co, and mixtures thereofwherein P comprises at least about 40 wt % of (PQR), Q is an alloyingmetal comprising Cr, Mn, and Al wherein Q comprises at least about 20 wt% of (PQR), wherein Cr is at a concentration of at least about 10 wt %,Mn is at a concentration of at least about 2.5 wt %, and Al is at aconcentration of at least about 2.0 wt % of said alloy (PQR), and R isan alloying element wherein R comprises about 0.01 wt % to about 5.0 wt% of (PQR).
 59. The alloy composition of claim 58, wherein said alloyingelement R is selected from the group consisting of B, C, N, Si, P, Ga,Ge, As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru,Rh, Ir, Pd, Pt, Cu, Ag, Au, and mixtures thereof.
 60. The alloycomposition of claim 58, wherein said metal P comprises at least about60 wt %, said alloying metal Q comprises at least about 30 wt %, andsaid alloying element R comprises about 1.0 wt % to about 5.0 wt % ofsaid alloy (PQR), wherein Cr is at a concentration of at least about 20wt %, Mn is at a concentration of at least about 7.5 wt %, and Al is ata concentration of at least about 4.0 wt % of said alloy (PQR).
 61. Analloy composition comprising an alloy (PQR), wherein P is a metalselected from the group consisting of Fe, Ni, Co, and mixtures thereofwherein P comprises at least about 40 wt % of (PQR), Q is an alloyingmetal comprising Cr, Mn, and Si wherein Q comprises at least about 20 wt% of (PQR), wherein Cr is at a concentration of at least about 10 wt %,Mn is at a concentration of at least about 2.5 wt %, and Si is at aconcentration of at least about 2.0 wt % of said alloy (PQR), and R isan alloying element wherein R comprises about 0.01 wt % to about 5.0 wt% of (PQR).
 62. The alloy composition of claim 61, wherein said alloyingelement R is selected from the group consisting of B, C, N, Al, P, Ga,Ge, As, In, Sn, Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru,Rh, Ir, Pd, Pt, Cu, Ag, Au, and mixtures thereof.
 63. The alloycomposition of claim 61, wherein said metal P comprises at least about60 wt %, said alloying metal Q comprises at least about 30 wt %, andsaid alloying element R comprises about 1.0 wt % to about 5.0 wt % ofsaid alloy (PQR), wherein Cr is at a concentration of at least about 20wt %, Mn is at a concentration of at least about 7.5 wt %, and Si is ata concentration of at least about 4.0 wt % of said alloy (PQR).
 64. Analloy composition comprising an alloy (PQR), wherein P is a metalselected from the group consisting of Fe, Ni, Co, and mixtures thereofwherein P comprises at least about 40 wt % of (PQR), Q is an alloyingmetal comprising Cr, Mn, Al, and Si wherein Q comprises at least about20 wt % of (PQR), wherein Cr is at a concentration of at least about 10wt %, Mn is at a concentration of at least about 2.5 wt %, Al is at aconcentration of at least about 2.0 wt %, and Si at a concentration ofat least 2.0 wt % of said alloy (PQR), and R is an alloying elementwherein R comprises about 0.01 wt % to about 5.0 wt % of (PQR).
 65. Thealloy composition of claim 64, wherein said alloying element R isselected from the group consisting of B, C, N, P, Ga, Ge, As, In, Sn,Sb, Pb, Sc, La, Y, Ce, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, Pd, Pt,Cu, Ag, Au, and mixtures thereof.
 66. The alloy composition of claim 64,wherein said metal P comprises at least about 60 wt %, said alloyingmetal Q comprises at least about 30 wt %, and said alloying element Rcomprises about 1.0 wt % to about 5.0 wt % of said alloy (PQR), whereinCr is at a concentration of at least about 20 wt %, Mn is at aconcentration of at least about 6 wt %, Al is at a concentration of atleast about 4.0 wt %, and Si is at a concentration of at least about 4.0wt % of said alloy (PQR).